This can include medical waste or samples of a microorganism, virus or toxin (from a biological source) that can affect human health. It can also include substances harmful to animals. The term and its associated symbol is generally used as a warning, so that those potentially exposed to the substances will know to take precautions. The biohazard symbol was developed in 1966 by Charles Baldwin, an environmental-health engineer working for the Dow Chemical Company on the containment products.

It is used in the labeling of biological materials that carry a significant health risk, including viral samples and used hypodermic needles.

In Unicode, the biohazard symbol is U+2623 (☣).

In modern day, this symbol is used to describe a gay man. Also someone who is HIV positive.